1. Field of the Invention
The present invention relates to a transmission X-ray analyzer, which is capable of measuring a transmission X-ray output from a sample through use of a time delay and integration (TDI) sensor.
2. Description of the Related Art
Conventionally, a foreign matter in a sample and density unevenness of elements have been detected by X-ray transmission imaging. As a method of the X-ray transmission imaging, there is known a method of converting a transmission X-ray output from a sample into fluorescent light through a fluorescent screen or the like, and detecting the fluorescent light through use of image pickup devices (charge coupled devices (CCDs)). As a detection method using CCDs, there is a method of scanning a sample to obtain linear images successively through use of a line sensor having a plurality of image pickup devices arranged in one direction, thereby obtaining a two-dimensional image of the sample.
By the way, when the movement speed of a sample in a transportation direction increases, the time period of accumulation of charge in the line sensor becomes shorter, and in the case where the sensitivity of the line sensor is low, an S/N ratio decreases. For this reason, a time delay and integration (TDI) sensor has been used, in which a plurality of (stages of) line sensors are arranged in parallel in the transportation direction and charge accumulated in one line sensor is transferred to an adjacent subsequent line sensor. In the TDI sensor, the charge accumulated in a line sensor of the first stage is transferred to a line sensor of the second stage. In a line sensor of the second stage, the charge transferred from the line sensor of the first stage is added to the charge accumulated when the line sensor of the second stage receives light, and the resultant charge is transferred to a line sensor of the third stage. Thus, charge transferred from a line sensor of the previous stage is added sequentially to each line sensor, and accumulated charge transferred to a line sensor of the last stage is output.
Accordingly, in the TDI sensor, in the case where the number of stages is T, charge which is T times as large as that of a single line sensor is accumulated, and a contrast becomes T times as high as that of a single line sensor. Further, noise is reduced, measurement can be performed at high speed, and an S/N ratio increases.
On the other hand, for example, an electrode of a lithium ion battery is produced continuously by unrolling a roll-shaped collector metal foil and applying an electrode material to the foil. Therefore, when a foreign matter in the strip-shaped electrode is detected by X-ray transmission imaging, the electrode is transported continuously to a position between an X-ray source and a sensor by transportation rollers, to thereby detect the foreign matter (Japanese Patent Application Laid-open No. 2004-614793 (FIG. 4)).
By the way, as described above, the TDI sensor has sensitivity higher than that of the line sensor. However, when a distance between a sample and a multi-stage TDI sensor until the sample passes along the TDI sensor changes by a predetermined amount, a feed speed of the sample differs significantly from a feed speed of a transmission image on the TDI sensor to cause displacement of a detection position, with the result that points to be detected are scattered. In this case, there is a problem in that charge is not accumulated conveniently, and an accumulated image is blurred to increase a minimum detectable size, resulting in remarkable degradation in detection accuracy.
In particular, in the case of measuring a transmission X-ray with the TDI sensor while transporting a band-shaped continuous sample as in the electrode of the lithium ion battery with transportation rollers, the sample may be transported to the TDI sensor in a fluttered state. Thus, the above-mentioned problem becomes remarkable.